Research on nutrition and growth in the culture of post larval turbot (Scophthalmus maximus L.)

A compilation of research data on post-larval nutrition and growth in turbot culture is given in order to outline this process and to highlight aspects deserving special attention in future research. The obtained growth rates as function of body weight give a fair indication of the maximum attainable growth in turbot culture. By using a mathematical description derived from these data, a growth protocol can be designed describing the desired growth of appproximately 2 kg in two years which can be used to set standards for growth performance of size groups in turbot culture. The steeply declining growth rate at increased body weight is easily explained by the maximum attainable feed intake rates in literature. Optimum feed composition in terms of percentage gross energy presented as protein is very high according to studies on juvenile turbot, although it declines rapidly at increasing fish size, indicating that more non-protein energy should be applied in diets for larger turbot. It is suggested that feeds for juvenile fish should have a higher protein to energy ratio than encountered in the present feeds. It is demonstrated that the characteristics of small fish, that are most commonly used in the nutrition studies, are of minor importance for the culture of turbot, whereas the poorly known characteristics of the larger size groups dominate the productivity and efficiency of turbot culture. Due to the low feed intake rate of the larger fish, dietary composition appears to influence the apparent protein efficiency significantly, whereas growth rate is only slightly influenced. This implies that an optimum dietary composition mainly results in lower feed costs and reduced environmental loading, but only moderately in an increased productivity. The feed intake rates encountered in die culture of larger turbot are within a range where any increase in feed intake leads to higher growth combined with lower feed conversions. It is recommended that special attention should be given to physical properties of the feed, combined with feeding methods which prevent feed spilling. It is demonstrated that only a slight spilling of feed can already double the waste discharge into the environment.